Security has been stepped up for today's Irish Grand National after a vitriolic slogan was burnt into the racecourse ahead of the visit of Queen Elizabeth.

Workers at Fairyhouse Racecourse in Co Meath immediately worked to block out the phrase which had been written in the grass with weedkiller near the finishing post in front of the main stand.

Peter Roe, the acting racecourse manager, said they were "shocked" by the incident but the vast majority of racegoers had been unaware of it.

The phrase -- 'F*** the queen' -- only became visible from a height to people in the stands at around midday yesterday after the weedkiller took effect and the grass turned brown.

Workers immediately spread bags of cut grass over the brown patches to camouflage the phrase.

Mr Roe said they were not aware who had done it and it may have been poured on the grass three to four days ago.

"We've done our best to sort it out. We'll have extra security on tonight. We've had security for the last two nights," he explained.

"This didn't happen yesterday, this happened a couple of days ago. This only came to light today," he added.

"We will up the security and garda presence as the National is very important. It is a national institution."

He said a lot of people also used the track for walking and it was highly disappointing.

Mr Roe said the matter had also been brought to the attention of the gardai.

Agriculture Minister Simon Coveney, who is presenting today's Ladbrokes Irish Grand National trophy, said yesterday: "I think it is sad that people are still so stuck in the past, that they might try to damage the reputation of the Irish horse racing industry by trying to get across what are totally outdated views that don't represent the views of anybody really left in Ireland."

Meath TD Shane McEntee, who is a Minister of State at the Department of Agriculture, said it was "pure nonsense" and people would "not put up with that".